I've been using Boss SD-1 overdrives for as long as I can remember. Having read all the hoop-la about the Keeley mods, I decided to play around with one of mine and do the mods myself. Personally I didn't find most of them to be very useful at all. I like the asymetrical clipping of the SD-1 so I changed the diodes back to that configuration. I didn't try the germanium transistor mod yet...That could be abig difference...who knows? Swapping the caps for more bass response definitely added bass but made it a little too 'woofy' I think, when running the drive up higher and level a bit lower. Used at full-on volume as a pure amp overdriver with the drive cut back it sounded better but at that point didn't seem like that much of an improvement over stock. Changingthe input impeadence didn't seem to do a heck of a lot either. Jumping the drive up worked well insofar as increasing it but I really didn't like the overall resulting sound.I guess I feel they have enough drive for their intended purpose. After swapping out some of the caps for MF type,I couldn't really tell a discernable difference in 'harshness' Something that did make a difference was the "stacked" 4558 mod. I tried using the Burr brown as the old mod called for and it gave a decidedly different response.The gain is smoother and more compressed sounding on lead lines, but I didn't care as much for it overall. I swapped out a few different op-amps and ended up liking the 'satcked' JRC4558 (which Keeleyis now using) best of all. Seems to have added clarity and reduced noise when A/B'd beside just a single 4558. This is not intended to be in any way a knock on Keeley's stuff, just sharing my experiences. Since I aped the mods off the net, there could be more to it than what I've found but I'm pretty sure I basically have everything. I'm going to play around with it some more and see if I can make any "improvements" that are just that.